1. Field of the Invention
This invention relates generally to a corona igniter for emitting a radio frequency electric field to ionize a fuel-air mixture and provide a corona discharge, and more particularly to controlling the temperature of the corona igniter during operation.
2. Related Art
A corona igniter of a corona discharge ignition system receives a voltage from a power source and emits an electrical field that forms a corona to ionize a mixture of fuel and air of an internal combustion engine. The igniter includes a central electrode extending longitudinally form an electrode terminal end to an electrode firing end. An insulator is disposed along the central electrode, and a shell is disposed along the insulator.
The electrode terminal end receives the voltage from the power source and the electrode firing end emits the electrical field that forms the corona. The electrical field includes at least one streamer, and typically a plurality of streamers forming the corona. The corona igniter does not include any grounded electrode element in close proximity to the electrode firing end. Rather, the mixture of air and fuel is ignited along the entire length of the high electrical field generated from the electrode firing end. An example of a corona igniter is disclosed in U.S. Patent Application Publication No. US 2010/0083942 to the present inventor, Lykowski et al.
In internal combustion engine applications, the temperature of the corona igniter, especially at the firing end, impacts ignition performance. Corona igniters of the prior art oftentimes reach undesirable temperatures at the firing end, such as temperatures greater than 950° C. Such high temperatures are likely to degrade the quality of ignition. The corona igniter can experience reduced endurance or other combustion problems.